1 Removal of Total Petroleum Hydrocarbons (TPHs) and Polycyclic 1 Aromatic Hydrocarbons (PAHs) in Spent Synthetic-Based Drilling 2 Mud 3 Using Organic Fertilizer 4 5 6 Abstract 7 Treatment and disposal of spent(used)drilling mud have become animportant environmental 8 challenge in the oil and gas industry. Total Petroleum Hydrocarbons (TPHs) and Polycyclic 9 Aromatic Hydrocarbons (PAHs) constitute the major contaminants in spent drilling mud. In this 10 study, five spentsynthetic-based drilling mud samples were collected from five oil fields in the 11 Niger Delta. Samples collected on day 0 were analyzed for TPHs and PAHs. Concentrations 12 higher than thepermissible regulatorylimits were recorded. The efficacy of urea fertilizer in the 13 remediation of TPH-and PAH-impacted mud was investigated. Six sub-samples and six control 14 sub-samples were tested bi-weekly for 12 weeks with 20g, 25g, and 30g doses of urea fertilizer per 15 20L of spent mud for each of the five samplesrepresenting each individual oil field (marked A 16 through E). Removal of TPHs and PAHs with urea fertilizer treatment proved to be fast and 17 efficient. In 6 weeks, with a dose of 1.5g/L, over 98% removal of TPHswas recorded, and more 18 than 94% of PAHs, and in 12 weeks, more than 99.5% removal was recorded for both. The 19 residual levels of TPHs and PAHs met Department of Petroleum Resources(DPR: Nigeria) and US 20 EPA limits for land disposal. Mathematical models with agoodness of fit(R 2 ) of 0.999, were 21 developed to predict the rate of thedegradation processes. 22 Keywords: Spent Drilling Mud, Niger Delta, Total Petroleum Hydrocarbons, and Polycyclic 23 Aromatic Hydrocarbons, Biodegradation, Urea Fertilizer, Mathematical Model. 24 25 1. INTRODUCTION 26 Drilling is one of the major chemical intensive operations in oilfields that generates wastes, which 27 can impact the environment. (Coussotet al., 2004; Ebrahimi et al., 2012; Zhang et al.,2011; Ball et 28 al., 2012; Hu et al., 2014). In drilling operations, two main types of wastes are generated, drill 29 cuttings and spent drilling mud(Mkpaoroetal.,2015;Bakke et al.,2013;Bamberger and 30 Oswald,2012;Bansal and Sugiarto,1999).Drilling fluids, including synthetic base fluids (SBFs), play 31 important roles in drilling operations by providing relatively better shale inhibition, lubricity, and 32 thermal stablity characteristics(Fomasieretal.,2017;Nahmad and Lepe, 2014;Ball et al., 2012). Other 33 SBF functions include lifting of drill cuttings from the well and controlling hydraulic pressure(Anon, 34 2011;Dankwaetal., 2018). 35
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1
Removal of Total Petroleum Hydrocarbons (TPHs) and Polycyclic 1
Aromatic Hydrocarbons (PAHs) in Spent Synthetic-Based Drilling 2
Mud 3
Using Organic Fertilizer 4
5
6
Abstract 7
Treatment and disposal of spent(used)drilling mud have become animportant environmental 8
challenge in the oil and gas industry. Total Petroleum Hydrocarbons (TPHs) and Polycyclic 9
Aromatic Hydrocarbons (PAHs) constitute the major contaminants in spent drilling mud. In this 10
study, five spentsynthetic-based drilling mud samples were collected from five oil fields in the 11
Niger Delta. Samples collected on day 0 were analyzed for TPHs and PAHs. Concentrations 12
higher than thepermissible regulatorylimits were recorded. The efficacy of urea fertilizer in the 13
remediation of TPH-and PAH-impacted mud was investigated. Six sub-samples and six control 14
sub-samples were tested bi-weekly for 12 weeks with 20g, 25g, and 30g doses of urea fertilizer per 15
20L of spent mud for each of the five samplesrepresenting each individual oil field (marked A 16
through E). Removal of TPHs and PAHs with urea fertilizer treatment proved to be fast and 17
efficient. In 6 weeks, with a dose of 1.5g/L, over 98% removal of TPHswas recorded, and more 18
than 94% of PAHs, and in 12 weeks, more than 99.5% removal was recorded for both. The 19
residual levels of TPHs and PAHs met Department of Petroleum Resources(DPR: Nigeria) and US 20
EPA limits for land disposal. Mathematical models with agoodness of fit(R2) of 0.999, were 21
developed to predict the rate of thedegradation processes. 22
Keywords: Spent Drilling Mud, Niger Delta, Total Petroleum Hydrocarbons, and Polycyclic 23
Total Petroleum Hydrocarbons(TPHs) and Polycyclic AromaticHydrocarbons(PAHs) are some of 36
the major contaminants of the spent drilling mud and they impact adversely on the environment if 37
carelessly disposedof(Fijałet al.,2015; Fontenot et al.,2013). Studies have shown that plant growth 38
is affected when petroleum hydrocarbon-impacted spent drillingmud is released on 39
land(Osisanya,2011). Levels of spent drilling mudabove a few percentages in soil (by weight) have 40
beenshown to degrade plant growth(Clements et al., 2010;Czekajet al.,2005). Improper disposal of 41
spent drilling mud into water bodiesendanger marine life (Anozie and Onwurah,2001).Safe 42
disposal of spentdrillng mud after drilling is a major problem in the oil and gas industry(Gross et 43
al.,2013; Hou et al.,2012;Onwukwe and Nwakaudu,2012). Most of the existing methods of 44
treatment like fixation,andthermal methods,have disadvantages ranging from high risk to personnel 45
to huge costs because of thehigh energy demands due to high temperature requirements(Liu et al., 46
2016;Kerri et al., 2013).Some of these existing methods of treatment require expensive and 47
sophisticated equipment with high capital and operating costs (Hu et al., 2014;Kerri et al.,2013; 48
Xieet al.,2015). 49
Bioremediation is the biological breakdown or biodegradation of contaminants(Bewley et al., 50
2001). It involves the microbial breakdown of organic compounds into less complex compounds, 51
mostly water, and carbon dioxide and sometimes methane(Patel et al., 2012). The rate and extent 52
of biodegradation depends on the population and type of microorganisms, the environment, and the 53
chemical structure of the contaminant(Semple et al., 2003). Most organic compounds are 54
biodegraded under aerobic conditions(Kauppi et al., 2011). Biodegradation of some organic 55
compounds has also occurred under anaerobic conditions, although at rates not as rapid as under 56
aerobic conditions(Akindeet al., 2012). Intrinsic bioremediation or natural attenuation is the 57
biodegradation of a target contaminant without intervention under an appropriate environmental 58
condition, available nutrients (mostly phosphate, nitrogen and sulfur), and 59
microorganisms(Ibieneet al., 2011). However, from regulatory point of view, the rate of intrinsic 60
bioremediation is slow because of time limits(Chikere et al., 2012b). As a result, enhanced 61
(engineered) bioremediation is required most of the time(Abdusalamet al.,2011;Kadaliet al., 62
2012). In engineered bioremediation, the rate of bioremediation is increased in two ways: 63
biostimulation and bioaugmentation(Abdusalamet al,2011;Bourceretet al., 2015). Biostimulation 64
3
was deployed in this study by use of urea fertilizer,as a source of nutrient to the indigenous 65
microorganisms, to biodegrade TPHs and PAHs in impacted, spent synthetic based mud. 66
Urea is one concentrated source of available nitrogen. It is widely used in agriculture as a fertilizer 67
and animal feed additive. Urea fertilizer is the most important nitrogenous fertilizer.It is called the 68
King of Fertilizers because of its high nitrogen content (about 46 percent). 69
It is a white crystalline organic chemical compound. It is neutral and can adapt to almost all the 70
land. It is a waste product formed naturally by metabolizing protein in humans as well as other 71
mammals, amphibians and some fish. The main function of urea fertilizer is to provide the plants 72
with nitrogen to promote green leafy growth. It can make the plants look lush, and it is necessary 73
for the photosynthesis of plants. Nitrogen is an important nutrient required for microbial growth. 74
Urea fertilizer is widely used in biostimulation because of its high nitrogen content. 75
Advantages of urea fertilizer include: highest nitrogen content (this percentage is much higher than 76
in other available nitrogenous fertilizers), low cost of production, no storage risk (not subject to 77
fire or explosion hazards), and wide application-urea fertilizer can be used for all types of crops 78
and soils and does not harm the soil. However, it is very soluble in water and hygroscopic, and 79
requires better packaging quality. 80
81 Mathematical models help to predict the expected outcome of experiments.This saves time and cost for 82
future jobs.More often the field and laboratory data are used to calibrate mulit- purpose regression models 83
of linear and/or higher order equivalence.The statistical approach was adopted in this study for model 84
development. 85
2. METHODOLOGY 86
2.1Area of Case Study 87
4
This study was carried out with spent, synthetic based mud (SBM) from five oilfields in the Niger 88
Delta. TheNiger Delta is located at an elevation of 96m above mean sea level. It lies between East 89 Longitude 5° and 8° and North Latitude 3° and 6°.Samples A, B, C, D and E were taken at 90 Longitude 5°9'40.58"East and Latitude5°19'17.71"North, Longitude 6°47'4.912"East and Latitude 91
3°11'37.644"North, Longitude 6°16'41.972"East and Latitude 4°11'42.948"North, Longitude 92 6°21'20.38"East and Latitude 4°54'28.648"North, Longitude 6°42'12.077"East and Latitude 93
4°59'30.057"North, respectively.( Figure 1.)The region has a population of 30 million people 94
(NBS,2006). Over 90% of Nigeria’s proven oil and gas reserves are located in the region ((Adati, 95 2012). The NigerDelta covers a coastline of 560km
2, and it is formed primarily by sediment 96
deposition(Osinowoet al,2018). It’s a rich mangrove swamp covering over 20,000km2 within 97
wetlands of 70,000km2 (Ekubo and Abowei,2011). Oil was first discovered in the delta by Royal 98
Dutch Shell (Shell Nigeria), formerly Shell-BP, in 1957 at Oloibiri, and production began in 1958. 99
The oil and gas industry play significant role in Nigeria’s economy, accounting for about 90% of 100
its gross income(Abubakar,2014). Figure 1 shows the map of Niger Delta and drilling mud sample 101 locations. 102
103
Figure 1. Location map of study area 104
105
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2.2 Data collection 106
Adequate quantities of the spent drillingmud from five oil fields were sampled from well-agitated 107
mud tanks and transported to the laboratory as quickly as possible to ensure that the parameters of 108
the mud did not change before testing. Convenience sampling method was used because of low 109
drilling activities in Nigeria,at the time of this study.In the laboratory, the samples were again 110
thoroughly agitated with sample mixers to ensure proper mixing.The samples were marked MUD-111
A to E and tested for baseline values of the physicochemical parameters (Table 2). For each 112
sample, 25 (twenty-five) sub samples of 20L each were created: (i) One sub-sample for baseline 113
studies; (ii) Eighteen (18) sub-samples for bioremediation treatment for Total Petroleum 114
Hydrocarbons(TPHs) and PAHs with urea fertilizer (6 sub-samples each for 20g, 25g, and 30g 115
doses); (iii) Six (6) sub-samples for control. The control samplesare the original spent drillingmud 116
without treatment. Urea fertilizer was used as a source of nutrients for the hydrocarbon utilizing 117
bacteria (HUB) for the remediation of the mud impacted with Total Petroleum Hydrocarbonsand 118
PAHs. Both the treated and control samples were tested bi-weekly for 12 weeks. The tests 119
conducted and methods used are shown in Table 1. 120
Table 1: Analytical methods employed in the study 121
Parameter Analytical Method STANDARD
TPHs and PAHs GC/FID (Agilent 7890A GC systems) ASTM D 3921
THB and HUB Total Plate Count ASTM D5465-16
Total Nitrogen Kjeldahl ASTM D8001-16e1
Temperature Meter reading ASTM E2251-14
pH Meter reading ASTM D1293-18
Moisture Content Gravimetric method ASTM D2216-98
CO2 Standard method for dissolved carbon
dioxide in liquid ASTM D513-16
DO Standard method for dissolved oxygen in
liquid ASTM D888-12e1
Phosphorous Total phosphorous-EPA method EPA 365.1
6
TOC Standard test method for total carbon and
organic carbon in liquid by ultraviolet and
infrared dictation
ASTM D4839-03(2017)
122
2.3 Predictive model 123
Nonlinear regression analyses were applied in modeling the duration of the effective biological 124
treatment of the spent drilling mud. XLSTAT 2018 was the statistical tool employed as an aid for 125
the model development (Ziegler, 2005; Nwaogazie, 2011). 126
127
3. RESULTS AND DISCUSSION 128
3.1 Results 129
Baseline physicochemical parameters of spent drilling mud samples 130
The baseline values of the physicochemical parameters of the spent drilling mud are shown in 131
Table 2. Nigerian and US EPA effluent limits for TPHs and PAHs are also shown in Table 3.It can 132
be seen that spent drilling mud from different oil wells have varying concentrations of the 133
contaminants. 134
135
Table 2: Physico-chemical parameters of the spent drilling muds 136
S/NO
Parameters
A
Sample
B
C
D
E
1 pH 7.5 ± 0.01b 7.3 ± 0.01
a 7.8 ± 0.00
c 7.4 ± 0.09
a 7.9 ± 0.00
c
2 Temperature(oC) 28 ± 0.00
a 28.3 ± 0.10
b 28.7 ± 0.05
c 29.0 ± 0.00
d 28.5 ± 0.10
bc
3 Nitrogen (mg/L) 0.06 ± 0.004b 0.08 ± 0.005
d 0.06 ± 0.004
b 0.04 ± 0.002
a 0.05 ± 0.003
ab
4 Potassium (mg/L) 2.0 ± 0.3ab
2.7 ± 0.3d 1.7 ± 0.2
a 2.2 ± 0.1
ab 2.0 ± 0.2
ab
5 Sodium (mg/L) 2.4 ± 0.03b 1.7 ± 0.02
a 2.3 ± 0.03
b 1.7 ± 0.10
a 2.4 ± 0.10
b
6 Calcium (mg/L) 13.4 ± 0.2a 16.3 ± 0.2
c 17.4 ± 0.00
d 14.7 ± 0.10
b 19.10 ± 0.2
e
7 Phosphate(mg/L) 2.3 ± 0.03a 7.4 ± 0.03
d 7.6 ± 0.05
e 5.8 ± 0.03
c 3.8 ± 0.04
b
8 Conductivity 2.58 ± 0.02a 2.68 ± 0.02
b 2.84 ± 0.03
c 2.62 ± 0.02
ab 2.86 ± 0.02
c
9 Chlorides (mg/L) 18.8 ± 0.2a 22.2 ± 0.4
b 23.3 ± 0.43
c 19.64 ± 0.04
a 25.47 ± 0.03
d
10 TOC (%) 1.4 ± 0.2a 1.8 ± 0.2
a 1.95 ± 0.3
a 2.0 ± 0.3
a 1.6 ± 0.3
a
11 DO (mg/L) 7.1 ± 0.3a 7.95 ± 0.45
a 10.4 ± 0.4
b 8.4 ± 0.5
a 7.2 ± 0.4
a
12 Moisture Content (%) 8.9 ± 0.6bc
9.2 ± 0.4bc
7.6 ± 0.3ab
10.3 ± 0.3c 6.8 ± 0.5
a
13 CO2 (mg/L) 1.6 ± 0.1a 1.8 ± 0.1
a 2.2 ± 0.2
a 1.7 ± 0.3
a 2.1 ± 0.4
a
7
14 TPHs (mg/L) 6211 ± 10a 8591 ± 8
c 9474 ± 10
d 10110 ± 10
e 7482 ± 8
b
15 PAHs(mg/L) 82.0 ± 0.5a 94.6 ± 0.4
d 84.7 ± 0.3
b 86.25 ± 0.55
b 92.6 ± 0.4
c
16 THB (CFU/ml) 9.4 ± 0.1×105e
7.6 ± 0.02×105a
8.4 ±0.01×104b
9.3 ± 0.0×105d
8.9 ± 0.05×105c
17 HUB (CFU/ml) 4.3 ± 0.1×104c
6.3 ±0.1×104a
5.2 ± 0.01×105d
6.4 ±0.1×104e
9.9 ± 0.01×104b
a-e
Results are presented as mean ± standard error. Means with different superscript, the 137
homogenous subset of means, (a, ab, b, bc, c, d and e) within the same rows indicate significant 138
differences (p < 0.05), 139
140
Legend: 141
DO = Dissolved Oxygen; 142
TOC=Total Organic Carbon; 143
TPHs=Total Petroleum Hydrocarbons; 144
PAHs=Polycyclic Aromatic Hydrocarbons; 145
HUB=Hydrocarbon Utilizing Bacteria, and; 146
THB=Total Heterotrophic Bacteria. 147
148
Table 3: DPR (Nigeria) and US EPA guidelines and standards for TPHs and PAHs 149